Breach of contract

This is to complain about Nashua mobile that had handed over my cell phone contract with them to mtn. Initial contract with nashua had a limit on amount that I would always receive on my phone for every monht. Somtime 2014 later I noticed that Nashua is no longer deducting the premium, mtn is deducting. When ever I phone eather of them I would get no answer and Nashua is no more to be found in Poetermaritzuburg where the contract was made and signed. On April 2014 I noticed that the balance that I'm required to pay mtn was R460. Why nashua never advised me when my contract was handed over to mtn because I only had contract with nashua not with mtn. Why nashua never advised mtn to limit my airtime like it was while I was on nashua. Now mtn had deducted this R460 and I ***** do not understand hance I say I asume mtn never limitted me on my contract that I never signed with them.